1. Field of the Invention
The present invention relates to a method and an apparatus for estimating an amount of drawn air of an internal-combustion engine. Further, the present invention relates to a method and an apparatus for controlling a value estimated by the above-mentioned method or apparatus for estimation, to a desired value. In particular, the present invention relates to a method and an apparatus for estimating an amount of drawn air, using an adaptive observer to identify a parameter and a method and an apparatus for controlling a value estimated by the above-mentioned method and apparatus for estimation, to a desired value.
2. Description of the Related Art
FIG. 1 shows a structure of an internal-combustion engine to which a method and an apparatus for estimating an amount of drawn air and a method and an apparatus for controlling a value estimated by the above-mentioned method and apparatus for estimation, to a desired value, according to the present invention, are applied. The internal-combustion engine in FIG. 1 is provided with charger comprising a turbine 2 and a compressor 1 and a flexible valve timing mechanism 8. The turbine 2 and the compressor 1 maybe mechanic or electrically connected. The flexible valve timing mechanism 8 may directly operate valves electrically or may electrically adjust valve operations carried out by mechanical cams. Further, in order to reduce emissions, the internal-combustion engine in FIG. 1 is provided with an airflow meter 3, an intake manifold pressure sensor (PB sensor) 6, a large area air-fuel ratio sensor (LAF sensor) 12, an oxygen sensor 15, a primary catalyst converter (highly heat-resistant and low thermal capacity CAT) 13 for early activation in sing stage and a main catalyst converter (high) cell density CAT) 14 for high cleaning-up ratio of emissions during a period after the engine has been warmed up. In FIG. 1, a charging pressure sensor, an electronically controlled throttle, an exhaust gas recycling valve, an injector, a combustion chamber and an ignition plug are represented respectively by reference numerals 4, 5, 7, 9, 10 and 11.
FIG. 2 shows an air-drawing section of the internal combustion engine. Air is fed through throttle 5 to the cylinder. FIG. 3 shows a relationship among an amount of air having passed through the throttle Gth, measured by the airflow meter 3, an amount of drawn air of the cylinder Gcyl, an amount of air firing the intake manifold Gb and an intake manifold pressure Pb measured by the intake manifold pressure sensor 6. FIG. 3 shows that an amount of air having passed through the throttle Gth will overshoot an amount of drawn air of the cylinder Gcyl, because of effect of fling the intake manifold. Accordingly, if an amount of air having passed through the throttle Gth is regarded as an amount of drawn air of the cylinder Gcyl to determine an amount of fuel to be injected, while the throttle is quickly moving, the air-fuel ratio will change as below. That is, the air fuel ratio will become too large (fuel is too rich) when the opening is increased and will become too small (fuel is too lean) when the opening is decreased. As a result, the cleaning-up ratio of a catalyst will be reduced
Conventionally, an amount of drawn air of the cylinder Gcyl has been estimated as mentioned below. A change in an amount of air filling the intake manifold ΔGB is estimated based on a change ΔPB in intake manifold pressure Pb, using the following equations.Pb(k)Vb=Gb(b)R Tb  (1)ΔPb(k)Vb=ΔGb(k)R Tb  (2)ΔGb(k)=ΔPb(k)Vb/(R Tb)  (3)
Vb, R, Tb and k respectively represent a volume of the intake manifold, the gas constant, gas temperature in the intake manifold and control time synchronized with intake stroke (TDC) of the cylinder. Tb is assumed to be constant.
A change in an amount of air filling the intake manifold ΔGb(k) is used to adjust an amount of air having passed through the throttle Gth(k) using the following equation to obtain an estimated value of an amount of drawn air of the cylinder Gcyl_hat(k).
 Gcyl—hat(k)=Gth(k)·ΔGb(k)  (4)
However, an effective volume of the intake manifold which contributes to the effect of filling the intake manifold, will vary depending on increase or decrease in the throttle opening and a changing rate of the throttle opening. Further, compensation for the overshot of an amount of air having passed through the throttle Gth, might be excessive or insufficient, as shown in FIG. 4, depending on a change in a gas temperature Tb in the intake manifold. In order to deal with the problem, gain scheduling has been performed for a volume of the intake manifold, an estimated value of an amount of drawn air of the cylinder Gcyl_hat(k) has been limited within limits or a change ΔGb in an amount of air firing the intake manifold has been subjected to filtering. As a result, the number of setting parameters for the above-mentioned methods has been increased. In spite of the efforts, the above-mentioned methods cannot deal with variation between engines or sensor properties and secular variation.
Publication of Japanese Unexamined Patent Application (KOKAI) No. 11-294231 discloses a method in which an estimated amount of drawn air is obtained using fuzzy-neural network. Refer to FIGS. 9 and 10 of the application. However, even this method cannot resolve the above-mentioned problems.
Accordingly, there is a great need fir a method and an apparatus for estimating an amount of drawn air, which can deal with variation between engines or sensor properties and secular variation, without increasing setting parameters. There is also a great need for a method and an apparatus for controlling a value estimated by the above-mentioned method and apparatus for estimation, to a desired value.